Glucose 6-phosphatase Activity Research Articles

Studies on the role of protein synthesis in cell injury by toxic agents: I. Effect of cycloheximide administration on several factors modulating carbon tetrachloride-induced liver necrosis

Cycloheximide pretreatment (1 mg/kg, ip) slightly attenuated the hepatic necrosis 24 hr after CCl 4 administration and this attenuation was more obvious at 72 hr. A dose of cycloheximide, 2 mg/kg, evoked a marked protective effect even at 24 hr. Cycloheximide administration (1 mg/kg) significantly reduced the body temperature in CCl 4-treated rats but did not change the CCl 4 concentrations in the liver. Prior treatment of the rats with cycloheximide decreased the amount of binding of 14CCl 4 to liver microsomal lipids and reduced CCl 4-induced lipid peroxidation at 1 hr but not at 6 hr after administration of the hepatotoxin. Cycloheximide did not alter the pentobarbital sleeping time of the rats nor did it interact with microsomes to give spectral changes. Cycloheximide did not alter microsomal cytochrome P-450 reductase activity. Administration of cycloheximide prior to CCl 4 did not prevent the CCl 4-induced decrease in cytochrome P-450 or glucose 6-phosphatase activity caused by the hepatotoxin. However it did prevent the CCl 4-induced polysome breakdown and it did attenuate the severity of the lesions caused by CCl 4 at the ultrastructural level.

Differential action of progesterones on hepatic microsomal activities in the rat

A significant reduction was found in the activity of drug-metabolizing enzymes (aminopyrine N-demethylase and coumarin 3-hydroxylase) and glucose 6-phosphatase in hepatic microsomes after the administration of reduced derivatives of progesterone (5α-pregnane-3β,-ol-20-one, 5β-pregnane-3α-ol-20-one, 5α-pregnane-3β,20β-diol and 5β-pregnane-3α,20α-diol) to rats. These steroids slightly raised inosine diphosphatase activity. On the other hand, 16α-hydroxyprogesterone and pregnenolone-16α-carbonitrile significantly increased drug metabolism and slightly elevated glucose 6-phosphatase. The contrasting action of the different progesterone derivatives was associated with changes in microsomal phospholipid synthesis. Pregnanolone and pregnanediol significantly decreased the de novo incorporation of [ 14C-Me]- l-methionine into microsomal phospholipids, mainly manifesting in phosphatidylcholine, phosphatidylethanolamine and lysophosphatidylcholine fractions; reduced the activity of S-adenosyl- l-methionine:microsomal-phosphatidylethanolamine methyl transferase; and caused a reduction of total microsomal phosphatidylcholine:phosphatidylethanolamine ratio. In contrast, 16α-hydroxy-progesterone and pregnenolone-16α-carbonitrile increased the de novo synthesis of microsomal phospholipids, methyl transferase activity and the ratio of total microsomal phosphatidylcholine: phosphatidylethanolamine. Treatment of rats with reduced progesterone derivatives diminished microsomal progesterone hydroxylation in the 16α- and 6β-position and raised progesterone Δ 4-5α-dehydrogenase activity measured in vitro. On the other hand, 16α-hydroxyprogesterone and pregnenolone-16α-carbonitrile elevated progesterone hydroxylation. Considering these opposite effects it can be postulated that in the rat the induction of drug-metabolizing activity of the hepatic endoplasmic reticulum might be controlled by a balance displayed in the synthesis and metabolism of various progesterone derivatives.

Microsomal membrane dysfunction in ischemic rat liver cells

To examine biochemically the effect of ischemia on cellular membranes, microsomal membrane structure and function in ischemic rat liver cells was studied. One-half hour of ischemia produced little or no evidence of histologic cell death 24 h after the reestablishment of blood flow and produced no detectable changes in five separate microsomal parameters measured in vitro. With 2 h of ischemia, histological evidence of liver cell death was quite marked 24 h after reflow had been established, and there were decreases in both microsomal calcium pump and glucose 6-phosphatase activities which could not be explained by differences in relative purity of the samples. Cytochrome P-450 content, glucuronyl transferase activity, and protein composition as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis in the 2-h ischemic microsomes were similar to those of 0.5-h ischemic preparations. These results indicate the presence of microsomal membrane dysfunction in ischemic rat liver cells temporally related to the onset of irreversible cellular damage. The possible molecular basis of this dyfunction is discussed.

Histological and histochemical studies on the rat brain under conditions of carbon disulfide intoxication

The brains of 35 male Wistar rats weighing 250 g were histologically and histochemically examined after a chronic intoxication due to five-month exposure to carbon disulfide. Morphologically, myelin sheath disruptions within the longitudinal tract systems of the spinal cord, destructions of individual ganglion cells in all brain regions and elective parenchyma necroses in the frontal and parietal cerebral cortices were found. The histochemical assays for enzyme activities of monoamine oxidase, ATPase, glucose 6-phosphatase, acetylcholine esterase and succinic dehydrogenase in the entire central nervous system revealed values identical to those obtained for control animals. Only succinic dehydrogenase and acetylcholine esterase revealed focal reduction in activities within the elective parenchyma necroses. After twenty-week duration of experiments a moderate decrease in activities of arylsulfatases and glutamic dehydrogenase in the entire central nervous system was found. Eventual causes responsible for these changes are discussed.

CYTOCHEMICAL LOCALIZATION OF GLUCOSE 6-PHOSPHATASE ACTIVITY IN THE LIVER OF GROWING MICE AFTER PHENOBARBITAL TREATMENT

The proliferation of the smooth-surfaced endoplasmic reticulum (SER) and the cytochemical localization of glucose 6-phosphatase (G6Pase) activity after phenobarbital treatment were observed in postnatal mouse livers showing rapid proliferation of SER and in adult livers. Animals received one daily intraperitoneal injection of phenobarbital for 3 or 5 days in a dosage of 35mg per kg of body weight for the first 3 days after birth, 50mg per kg for 3 to 9 days after birth, and 50 or 100mg per kg for the adult.Administration of phenobarbital to growing animals did not change the histochemical distribution of G6Pase activity within the liver lobule in contrast with reduction observed in the centrolobular activity in adult animals after the same dose of phenobarbital. An extensive proliferation of SER was noticed in centrolobular hepatocytes from adult animals treated with 100mg per kg of phenobarbital, while no such proliferation occurred after treatment with 50mg per kg of phenobarbital. However, centrolobular hepatocytes of 5- to 10-day-old animals showed a marked proliferation of SER with 50mg per kg of phenobarbital. These observations suggest that there are some differences in the nature of the phenobarbital-induced proliferation of SER between hepatocytes during the postnatal period and fully differentiated hepatocytes of the adult.

Intracellular calcium homeostasis in galactosamine-intoxicated rat liver cells: Active sequestration of calcium by microsomes and mitochondria

Active transport of Ca 2+ by isolated microsomes and mitochondria from galactosamine-intoxicated rat liver cells was studied. The aim was to determine the respective role of each organelle in the disturbed intracellular Ca 2+ homeostasis induced by this hepatotoxin. Calcium uptake by isolated microsomes is ATP dependent and oxalate augmented with a V of 1.45 nmol of Ca 2+/mg of microsomal protein/mm at 25 °C and an apparent K m for free Ca 2+ of 2.4 μ m. Concentrations of total Ca 2+ higher than 40 μ m are inhibitory. Two hours after administration of galactosamine (200 or 400 mg/kg), at a time when the total cell Ca 2+ content has increased, microsomes isolated from the treated animals exhibited no impairment in calcium transport. The microsomal preparations from the galactosamine-treated animals also had the same content of cytochrome P-450 and the same specific activity of glucose 6-phosphatase as those from the control animals. Calcium uptake by isolated liver mitochondria is also ATP dependent but virtually completely inhibited by 5 m m sodium azide. The V is higher than that of the microsomes, 20.5 nmol of Ca 2+/mg of protein/min at 25 °C, but the apparent K m for free Ca 2+ is similar, 5.7 μ m There was no alteration in the Ca 2+ uptake activity of mitochondria isolated from galactosamine-treated animals. These results imply that the initial disturbance in intracellular Ca 2+ homeostasis induced by galactosamine is entirely a consequence of the previously described plasma membrane injury. The potential significance of the observed kinetic properties of microsomes and mitochondria with regard to their respective roles in intracellular Ca 2+ homeostasis is discussed.

Effects of subacute and chronic lead treatment on glucose homeostasis and renal cyclic AMP metabolism in rats

The effects of chronic oral ingestion of lead in doses ranging from 20–80 ppm were compared with those seen after the subacute exposure of rats to a 10 mg/kg daily dose of the heavy metal for 7 days. Irrespective of the treatment regimen used, lead treatment significantly increased the activities of renal pyruvate carboxylase, phosphoenopyruvate carboxykinase, fructose 1,6-diphosphatase and glucose 6-phosphatase. The observed enhancement of kidney gluconeogenic enzymes in chronically treated animal was associated with a stimulation of the adenylate cyclase-cyclic AMP system, a rise in blood glucose and urea as well as a depression in hepatic glycogen and serum immunoreactive insulin (IRI) levels. In contrast, subacute exposure to lead failed to significantly alter cyclic AMP metabolism and the concentrations of liver glycogen, blood glucose, serum urea or IRI. Whereas the insulinogenic index (the ratio of serum IRI to blood concentration) was markedly suppressed in chronically treated rats, this ratio remained within normal limits following subacute exposure to the heavy metal. However, a marked decrease in the insulinogenic index was observed in subacutely treated rats 15 min after the administration of a glucose load. The data provide evidence to show that increased glucose synthesis as well as suppressed pancreatic function may be responsible for lead-induced disturbances in glucose homeostasis.

The Uptake and Metabolism of Glucose, Maltose and Starch by the Rumen Ciliate Epidinium ecaudatum caudatum

[14C]Glucose taken up by Epidinium ecaudatum caudatum was found in the pool, in the protozoal polysaccharide and in the bacteria associated with the protozoa. The amount incorporated into the polysaccharide depended on the square of the glucose concentration. Evidence was obtained that glucose was probably taken up initially into the pool unchanged, and then rapidly converted into glucose 6-phosphate and maltose which were subsequently hydrolysed to glucose. [14C]-Maltose was taken up at 20 to 30% of the rate of [14C]glucose, with 14C appearing initially in maltose and glucose 6-phosphate. 14C from 14C-labelled soluble starch appeared in the pool as maltose, glucose 6-phosphate and glucose in that order, but incorporation into protozoal polysaccaride was poor. Hexokinase, phosphoglucomutase, alpha-glucan and maltose phosphorylases, glucose 6-phosphatase and maltase activities were found in the protozoa.

The postnatal development of gluconeogenic enzymes in guinea-pig kidney cortex

The capacity for gluconeogenesis in the mammalian kidney has been assumed to be less than that in liver [1] and in man assumes importance only in prolonged starvation [2]. On the other hand, the observations of Alleyne [3] and Goodman [4] have suggested that the rise in gluconeogenic capacity seen in animals with metabolic acidosis is due to the fact that gluconeogenesis and the ability of the kidney to secrete H ÷ are somehow enhanced. The postnatal development of gluconeogenic enzymes in the kidney has been only partially investigated. Thus, the activities of glucose 6-phosphatase (EC 3.1.3.9.) and phosphoenolpyruvate carboxykinase (EC 4.1.1.36.) in the newborn rat kidney have been shown to increase quite substantially in the period following birth [5]. On the other hand, no detailed study of the development of gluconeogenic enzymes in the liver of animals with a bimodal distribution of phosphoenolpyruvate carboxykinase such as the guinea-pig have been reported until recently [6]. We report in this communication the appearance of key gluconeogenic enzymes in guinea-pig kidney in the period following birth.

Some cases of type III glycogen storage disease

Five patients with glycogen storage disease are described. Hypoglycemia was observed in all patients after an overnight fast, and glycemic and lactatemic curves obtained after oral administration of glucose or galactose were typical of those seen in Type III glycogenosis. An increase of liver glycogen up to 12–16% and complete absence of liver amylo-1,6-glucosidase were found in liver tissue samples obtained by needle biopsy. The patients were diagnosed as having Type III glycogenosis. In two patients the absence of amylo-1,6-glucosidase was accompanied by a sharp decline of liver phosphorylase activity. In one patient a decline of glucose6-phosphatase activity was observed. The structure of liver glycogen was different in different patients, and so were the types of glycemic and lactatemic curves obtained upon protein tolerance tests. The above phenomena might be explained by some secondary disturbances in the activity of enzymes (phosphorylase, glucose-6-phosphatase) involved in the metabolism of liver of these patients.

Precocious development of glucuronidating and hydroxylating enzymes in chick embryos treated with pituitary grafts.

1. Initiation of precocious development of UDP-glucuronyltransferase by an endogenous factor is reported for the first time. 2. This development occurs in chick embryo liver and kidney after grafting of the cephalic lobe of chicken pars-distalis pituitary tissue on to the chorioallantoic membrane, and in liver results in a rise in the enzyme activity from virtually zero to ;adult' values. Aniline hydroxylase also precociously develops in the liver of grafted embryos, its activity rising from one-third to the full adult value. Specific activities of glucose 6-phosphatase, cytochrome P-450 and NADPH-cytochrome c reductase did not significantly change. 3. The response of the transferase does not require the presence of host pituitary gland nor, apart from 1 day's necessary initiation, the presence of the graft itself. 4. The host becomes competent to respond on the 14th day of incubation; response continues for at least 3 days after removal of the graft, and for 2 days in the isolated liver. Grafting of embryonic pars distalis younger than 17 days does not evoke a response in the host liver. 5. Secretion of the pituitary factor increases suddenly some 24-48h before the naturally developing surge in liver UDP-glucuronyltransferase activity and may be responsible for initiating this rise in vivo. 6. The factor is probably not a growth or luteinizing hormone; its nature and the likelihood of a secondary hormone acting directly on the liver are discussed.

Inhibition of glucose 6-phosphatase by pure and impure C-type phospholipases. Reactivation by phospholipid dispersions and protection by serum albumin

1. Pure or impure C-type phospholipases hydrolysed rat liver microsomal phosphatides in situ at 5 degrees or 37 degrees C. At 5 degrees C mean hydrolysis of total phospholipids was 90% by Bacillus cereus and 75% by Clostridium perfringens (Clostridium welchii) C-type phospholipases. 2. Four degrees of inhibition of glucose 6-phosphatase (D-glucose 6-phosphate phosphohydrolase; EC 3.1.3.9) resulted. (a) At 37 degrees C inhibition was virtually complete and apparently irreversible. (b) At 5 degrees C phospholipase C inhibited 50-87% of the activity expressed by intact control microsomal fractions. (c) Bovine serum albumin present during delipidation alleviated most of this inhibition: at 5 degrees C phospholipase C plus bovine serum albumin inhibited by 0-35% (mean 18%):simultaneous stimulation by the destruction of its latency seems to offset glucose 6-phosphatase inhibition, sometimes completely. (d) If latency was first destroyed, phospholipase C plus bovine serum albumin inhibited 30-50% of total glucose 6-phosphatase activity at 5 degrees C. Only this inhibition is likely largely to reflect the lower availability of phospholipids, essential for maximal enzyme activity, as it is virtually completely reversed by added phospholipid dispersions. Co-dispersions of phosphatidylserine plus phosphatidylcholine (1:1, w/w) were especially effective but Triton X-100 was unable effectively to restore activity. 3. Considerable glucose 6-phosphatase activity survived 240min of treatment with phospholipase C at 5 degrees C, but in the absence of substrate or at physiological glucose 6-phosphate concentrations the delipidated enzyme was completely inactivated within 10min at 37 degrees C. However, 80mM-glucose 6-phosphate stabilized it and phospholipid dispersions substantially restored thermal stability. 4. It is concluded that glucose 6-phosphatase is at least partly phospholipid-dependent, and complete dependence is not excluded. For reasons discussed it is impossible yet to be certain which phospholipid class(es) the enzyme requires for activity.

Effect of Bile-Duct Ligation on Organelle Marker Enzymes in the Liver and Serum of Rats

1. Marker enzymes for the principal subcellular organelles of rat liver were asayed in the liver of rats 1 day and 8 days after bile-duct ligation or after laparotomy as a control procedure. 2. The microsomal enzymes in liver tissue showed complex changes. Benz[alpha]pyrene hydroxylase activity, predominantly found in the smooth endoplasmic reticulum, was decreased. Glucose 6-phosphatase activity and ribonucleic acid, which are localized predominantly in the rough endoplasmic reticulum, were increased. 3. The plasma membrane enzyme, alkaline phosphatase, increased in activity after bile-duct ligation. 4. No changes in mitochondrial enzyme activities were noted after 1 day but there was a 50% reduction 8 days after ligation. Lysosomal enzyme activities did not change in the liver tissue. 5. Liver catalase and D-amino acid oxidase activities showed a slight increase at 1 day postligation but a significant fall by 8 days. 6. Lactate dehydrogenase, a cytosol enzyme, showed a decrease in activity after 1 day but an increase in tissue activities 8 days after ligation. 7. Serum activities of mitochondrial, plasma membrane, microsomal, lysosomal and cytosol marker enzymes tended to increase post-ligation, particularly at 8 days. 8. Monoamine oxidase, a predominantly mitochondrial enzyme, was greatly elevated in the serum after 1 day but had returned to normal activities by 8 days.

Postnatal changes in the localization of glucose 6‐phosphatase activity within the liver lobule of the mouse

The change in the localization of glucose 6-phosphatase activity within the liver lobule of the mouse was studied during development. From one day before birth to three days after birth, a uniform localization of the activity was observed throughout the lobule. This uniform localization of the acitvity gradually changed to that of the adult type, characterized by a relatively higher activity in periportal areas, between three to ten days of age. This indicates that the postnatal growth of the liver is accompanied by a change in the pattern of the localization of this enzyme activity within the liver lobule. Further, the biochemical results showed that the elevated activity after birth was reduced to the level seen in adult at ten days of age. Thus, the reduction in the level of the enzyme activity during ten days after birth corresponds to a redistribution of the enzyme activity within the liver lobule.

Subcellular distribution of phospholipids during liver damage induced by rare earths

After intravenous injection of praseodymium nitrate, female Wistar rats develop fatty livers. In contrast to the marked increase of triglycerides, the phospholipid content was only increased by 50%. The subcellular distribution of phospholipids showed that major changes occur in the microsomal fraction within the first 24 hrs. Among the individual phospholipids only phosphatidylcholine and phosphatidylethanolamine concentrations were elevated. Further subfractioning revealed that phospholipid concentration increased in the smooth endoplasmic reticulum, whereas it decreased in the rough endoplasmic reticulum. The individual phospholipids in the smooth endoplasmic reticulum increased to the same degree as did the total phospholipids. On the other hand, in the rough endoplasmic reticulum only the lecithin fraction decreased, while all other phospholipids remained unchanged. Cytochrome P450, cytochrome b5, and glucose 6-phosphatase activity were drastically reduced in the rough endoplasmic reticulum, while no changes could be observed in the smooth endoplasmic reticulum. In the serum, phospholipid concentration fell to half the normal value within the first 24 hrs after praseodymium intoxication.

Sensitivity of glucose 6-phosphatase activity to glutaraldehyde

The effect of glutaraldehyde fixation on glucose 6-phosphatase activity in mouse liver was investigated. After transparenchymal perfusion with 2% glutaraldehyde for 1.5 minutes, the activity of the recovered enzyme was higher than those reported for acid phosphatase and aryl sulfatase activities after fixation under similar condition, and an abundant deposition of reaction product was observed in hepatocytes. Subsequent immersion in the same fixative solution for 30 minutes after 4 degrees C resulted in only a slight decrease in the activity. However, the activity was almost completely destroyed after 3 hours of immersion fixation at 4 degrees C following the perfusion. Therefore, the enzyme can be said to be aldehyde-sensitive when a long fixation time is used, but not aldehyde-sensitive during a short fixation time.

Relipidation of phospholipid-depleted microsomal particles with high glucose 6-phosphatase activity.

Microsomal particles enriched up to 20-fold in glucose 6-phosphatase activity (as compared to crude microsomal fractions) were prepared from livers of phenobarbital-treated, normal, and diabetic rats by a method involving sucrose-density gradient centrifugation through a layer containing deoxycholate, followed by flotation of the delipidated particles in a phospholipid-detergent mixture. The flotation with phospholipid resulted in the extraction of additional protein, in a corresponding increase in specific activity, and in relipidation of the particles to their original phospholipid content. Detergents alone did not extract any additional protein. Relipidation caused a change in the properties of the microsomal membrane, as indicated by a 4-fold decrease in the K(m) for glucose 6-phosphate and mannose 6-phosphate. The maximal rate was not affected. The crude homogenate of diabetic rat liver contained more latent enzyme than that of normal rats. The diabetic rats also yielded purified microsomal particles of specific glucose 6-phosphatase activity twice that of normal and five times that of phenobarbital-treated rats, indicating that some regulatory mechanism exists for the incorporation of different amounts of the enzyme into the endoplasmic reticulum.

Role of cyclic adenosine 3':5'-monophosphate in the action of 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane (DDT)on hepatic and renal metabolism.

The possibility whether alterations in the cyclic AMP-adenylate cyclase-phosphodiesterase system play a role in the action of 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane (DDT) on hepatic and renal carbohydrate metabolism was investigated. Administration of exogenous cyclic AMP (10mg/100g) was found to mimic the action of DDT which enhanced the activities of pyruvate carboxylase, phosphoenolpyruvate carboxylase, fructose 1,6-diphosphatase and glucose 6-phosphatase in both liver and kidney cortex, elevated the concentration of blood glucose and urea and decreased the amount of hepatic glycogen. Treatment with theophylline augmented the effects of a submaximal dose of this halogenated hydrocarbon on serum urea and glucose as well as the key gluconeogenic enzymes in liver and kidney cortex. Addition of DDT in vitro to liver and kidney homogenates resulted in a significant enhancement of adenylate cyclase activity. Hepatic and renal slices from rats already treated with DDT displayed an increased ability to convert [(3)H]adenosine into cyclic [(3)H]AMP. Whereas kidney-cortex slices excised from rats given caffeine and DDT produced an even greater amount of cyclic [(3)H]AMP, imidazole, propranolol and hydrazine prevented the insecticide-stimulated rise in cyclic nucleotide production. In contrast, prostaglandin E(1) failed to exert any significant effect on DDT-induced increases in cyclic [(3)H]AMP synthesis from radioactive adenosine. The present study and our previous findings (Kacew & Singhal, 1973e) support the concept that the DDT-induced alterations in carbohydrate metabolism of liver and kidney cortex may be related to an initial stimulation of the cyclic AMP-adenylate cyclase system in these tissues.

The Presence of Two Protein Phosphokinase Enzymes in Cod (Gadus callarius) Islet Membranes

The plasma membranes of cod islet cells have been shown to contain both an ATPdependent and a GTP-dependent protein phosphokinase. The ATP-dependent enzyme is stimulated by cyclic AMP, glucose 6-phosphate, phosphoenolpyruvate and ouabain. The GTP-dependent enzyme was not affected by cyclic AMP, glucose 6-phosphate or phosphoenolpyruvate but was strongly inhibited by ATP. The plasma membrane of mouse /?-cells has been shown to contain adenylate cyclase and phosphodiesterase (Davis & Lazarus, 1972). The presence of these enzymes suggests that cyclic AMP may play a role in insulin secretion at the membrane. The most likely effector site for cyclic AMP is a protein phosphokinase. The purpose of the present study was to determine whether a protein phosphokinase enzyme was present in the membrane and also to determine the factors modulating its activity. Cod islets were used as a model for this study since large amounts of tissue were required. The islets were homogenized and fractionated into nuclear mitochondrial, heavy microsomal(5000-20000g), microsomal and soluble fractions. The microsomal fraction was then treated with 0.7% (w/v) sodium deoxycholate and centrifuged at 20000g. The supernatant was then dialysed against Tris-HC1 buffer, pH7.4, and used for the experiments. Enzyme markers showed that 71 %of the 5’-nucleotidase activity of the original hornogenate was present in the deoxycholate-solubilized fraction. This fraction also showed high adenylate cyclase and adenosine triphosphatase activity. Glucose 6-phosphatase activity was mostly found in the 500&20000g fraction and in the pellet remaining after deoxycholate solubilization; only 2% of the total homogenate activity was found in the prepared membrane fraction. The specific activity of the ATP-dependent protein phosphokinase was trebled after deoxycholate treatment of the rnicrosomal fraction. The assay was based on the rate of transfer of 32P from [Y~~P-]ATP or [Y-~~PIGTP to acid-precipitable protein (Kuo et at., 1970). The optimum temperature for the enzyme was 15°C and the pH optimum 6.5. Table 1 shows the effect of various substances on the incorporation of 32P into membrane proteins by the ATP-specific enzyme. Cyclic AMP was a potent stimulator of the enzyme. Its effect was abolished by the addition of a specific antibody for cyclic AMP. Glucose 6-phosphate and phosphoenolpyruvate were powerful stimulators of phosphorylation. Other hexose phosphates and pentose phosphates and intermediates of glycolysis were without effect. Ouabain,

Sites of X-Irradiation-Induced Damage in the Microsomal Drug Metabolizing Enzyme System of Rat Liver during Development

The effect of x-irradiation at weaning stage on the activity of hexobarbital hydroxylation in male rate liver was studied during development. The increase of activity at the postweaning period was suppressed partially by 200 R irradiation and completely by 400 R, without remarkable change in the microsomal protein content of liver. Activities of microsomal electron transport system were inhibited only slightly at 40 days of age in 400 R irradiated rats, but both content of cytochrome P-450 and spectral change induced by hexobarbital were suppressed considerably. The activity of hexobarbital hydroxylation relative to the magnitude of cytochrome P-450 spectral change was about 60% lower than that of control. Adenosine triphosphatase and inosine diphosphatase activities were rather higher than those of control, while glucose 6-phosphatase activity was lower than that of control at 40 days of age in irradiated rats. Results are discussed in relation to the mechanism of effects of x-irradiation on the differen...